The present invention relates to an audio accessory circuit for providing a stereophonic reproduced sound with a presence sensation.
Input stereophonic signals may have conventionally been subjected to so-called surround processing for providing a stereophonic reproduced sound with a presence. The surround processing is usually performed by obtaining the difference between, for example, stereophonic L (left) and R (right) channel signals and changing the phase of the obtained difference signal.
An audio accessory apparatus for performing the surround processing comprising a subtracting circuit for obtaining the difference signal components from stereophonic input signals, a delay circuit for delaying the output signal from the subtracting circuit by a desired delay time and a level control circuit for amplifying or attenuating the output signal from the delay circuit so that the output of the level control circuit is added to said stereophonic input signals for outputting the added signals is disclosed in, for example, Japanese Unexamined Utility Model publication No. 61-93100.
However, a number of coils and capacitors are usually necessary for a delay element which forms a delay circuit used for the audio accessory apparatus disclosed in the above-mentioned publication. Accordingly, the structure of the whole of the apparatus becomes complicated and expensive. The audio accessory apparatus disclosed in the above-mentioned publication has a four-channel type output. This also causes the system to become complicated and expensive.
Recently, miniaturization of stereophonic reproducing apparatus has been strongly demanded. Accordingly, efforts for forming the audio accessory circuit for performing the surround processing of ICs have been made. The audio accessory circuit made of ICs are formed in such a manner that input stereophonic signals are passed through band pass filters having different pass bands and the gain of each band pass filter is controlled in response to the detected level of the component of each resultant frequency band.
However, the audio accessory circuit made of ICs requires a number of external parts, resulting in a complicated structure.
Therefore, the present invention was proposed under the above-mentioned circumstances. It is an object of the present invention to provide an audio accessory circuit having a simple and inexpensive structure in which the number of external parts can be reduced even if the circuit is made of ICs.
The audio accessory circuit of the present invention was proposed to accomplish the above-mentioned object and comprises subtracting means for outputting the difference signal between stereophonic input L and R channel signals variable gain band pass means for passing only frequency components of a given band from the output of said subtracting means and for desirably changing the gain of the frequency components to be passed; and adding means for adding the output of the variable gain band pass means to the signals of the input L and R channels.
The variable gain band pass means passes the components in high and low frequency bands and desiredly changes the gains of these frequency components.
In accordance with the present invention, reproduced sound is provided with presence by changing the gain of the components in a given frequency band, in particular, the components in a high frequency band over a wide range to emphasize the sound in the high frequency band and the reproduced sound is provided with massive sensation by changing the gain of the components in a low frequency band over a wide range to emphasize the sound in the low frequency band.